Method and apparatus for memory self testing

ABSTRACT

A self-test controller  10  is responsive to scanned in self-test instructions to carry out test operations including generating a sequence of memory addresses that is specified by the self-test instruction. Combining multiple such self-test instructions allows a custom test methodology to be built up by a user using a generic self-test controller  10.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to the field of data processing systems. More particularly, this invention relates to the self-testing of memories within data processing systems to detect memory defects.

[0003] 2. Description of the Prior Art

[0004] It is known to provide data processing systems incorporating memories with self-testing mechanisms, sometimes termed built-in self-test (BIST), such that when the memory circuits have been fabricated they may conduct a self-test or series of self-tests to determine if there are any memory defects present that would indicate that the circuit should be rejected. It is important that memory circuits should be highly reliable and that defective circuits should be effectively identified. As memory sizes increase, the proportion of the die being taken up by the memory is also increasing and, furthermore, the high transistor density within memory means that the defect density of these memories is becoming increasingly significant.

[0005] The type of defect that can arise may vary significantly from design to design and with different fabrication processes applied to the same design. For this reason, self-test methodologies are normally selected and tuned to a particular design and fabrication technique by the manufacturer concerned. A manufacturer will typically have their own preferred test methodology that experience has told them is well suited to their particular environment to identify defective memories. The test methodology adopted by one manufacturer may well not work well for another manufacturer.

[0006] It will be appreciated that self-test circuits whilst necessary to ensure a memory has been correctly fabricated, do represent a circuit area overhead that should be desirably reduced. The self-test circuits are typically used when an integrated circuit is manufactured but thereafter are not used during the normal operation of the integrated circuit.

SUMMARY OF THE INVENTION

[0007] Viewed from one aspect the present invention provides apparatus for processing data, said apparatus comprising:

[0008] at least one memory having a plurality of memory storage locations associated with respective memory addresses; and

[0009] a self-test controller operable to control self-test of said at least one memory; wherein

[0010] said self-test controller is responsive to a self-test instruction to perform at least one memory access to each memory location within a sequence of memory storage locations, memory address changes between successive memory locations accessed within said sequence of memory storage locations being selected in dependence upon said self-test instruction such that said self-test controller may be configured by said self-test instruction to implement different memory test methodologies.

[0011] The invention recognizes that in some circumstances a programmable self-test controller that allows different test methodologies to be performed by varying the address sequencing is desirable. In particular, providing a self-test controller that is programmable in this way enables the design of the self-test controller to be reused by various different manufacturers and yet allows those manufacturers to program the self-test controller to carry out a test methodology they select as best suited to their particular circumstances. Whilst providing a programmable self-test controller as opposed to one that can carry out merely one fixed test methodology does slightly increase the size and complexity of the self-test controller in a manner that would generally be regarded as disadvantageous, in practice this disadvantage is more than outweighed by the ability to reuse the self-test controller design to cope with the different test requirements of different manufacturers or the different test requirements that may arise for a single manufacturer as they evolve their own fabrication processes.

[0012] Whilst it would be possible for the self-test instructions to represent complete test methodologies, in preferred embodiments of the invention a plurality of self-test instructions are executed to perform a sequence of memory tests that may be adjusted to allow different sequences to be specified by different users. The self-test controller is effectively driven by a program of self-test instructions to carry out whatever test methodology is desired by a particular user.

[0013] It will be appreciated that the sequence of memory tests may be adjusted to suit the particular type of memory being tested or to suit a particular fabrication test methodology.

[0014] It will be appreciated that the memory addresses that are produced by the self-test controller could take a variety of forms and be mapped to the memory locations in different ways. However, many types of memory defects are associated with the physical location of a memory location in itself or relative to other memory locations and accordingly memory addresses that directly represent row and column addresses that give a physical position for the memory location are particularly well suited for generation by the self-test controller since the sequences of memory addresses that are useful in testing will generally be more easily formed when the memory addresses are represented in this way.

[0015] An important consideration with such a programmable self-test controller is deciding which addresses sequences and tests should be supported by the instructions provided. The instructions should be selected such that they can be combined in a wide range of different ways to provide a broad coverage of possible test methodologies that can encompass the requirements of many different situations. Weighed against this requirement, the greater the number of self-test instructions supported and the complexity of the tests they represent, the greater will be the complexity and overhead associated with the self-test controller. With the above factors in mind, preferred embodiments of the invention incorporate self-test instructions allowing the following test operations to be performed:

[0016] (i) write specified data to all memory locations within a range of memory addresses;

[0017] (ii) read data from all memory locations within a range of memory addresses;

[0018] (iii) write specified data to memory locations having a checkerboard pattern of memory addresses;

[0019] (iv) read data from memory locations having a checkerboard pattern of memory addresses;

[0020] (v) conduct a march C memory test;

[0021] (vi) read data from and write specified data to a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a row of memory locations are accessed in turn before a next row of memory locations is selected for access;

[0022] (vii) read data from and write specified data to a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a column of memory locations are accessed in turn before a next column of memory locations is selected for access;

[0023] (viii) read data from, write specified data to and read data from a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a row of memory locations are accessed in turn before a next row of memory locations is selected for access;

[0024] (ix) read data from, write specified data to and read data from to a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a column of memory locations are accessed in turn before a next column of memory locations is selected for access;

[0025] (x) for a sequence of memory locations, repeatedly write a value to one or more bitlines within said memory and then read a complementary value stored within a memory location sharing said one or more bitlines; and

[0026] (xi) for a sequence of memory locations, repeatedly read a value from a memory location while interjecting opposing data writes;

[0027] (xii) a predetermined combination of memory test operations as defined in (i) to (xi) for go/nogo testing where manufacture's test methods do not have specific requirements; and

[0028] (xiii) creating false read data at specific points in order to validate fail detection.

[0029] The invention is particularly well suited to use with embodiments in which the self-test controller, the one or more memories and a processor core are formed together on an integrated circuit. The increased use of relatively large amounts of memory fabricated on the same integrated circuit as a processor core leads to an increase in the need to support a larger number of test methodologies since the number of manufacturers of components incorporating significant amounts of memory is increased and the variations in the fabrication characteristics applied to different integrated circuits also increases. Looked at in another way, the technique responds to the change whereby memory is less frequently provided in the form of discrete integrated circuits produced by specialist memory manufacturers and is more generally incorporated within a single integrated circuit together with various other components, particularly processor cores, by a wider range of manufacturers, such as ASIC producers.

[0030] It will be appreciated that the memories to be tested could take a variety of different forms. In particular, the memories could be custom memories or synthesized memories depending upon the particular circumstances, each of these different types potentially require different test methodologies that are facilitated by the programmable nature of the self-test controller.

[0031] A further complication with the present technique is that different memories may require different signal values and timings in order to drive them. The desire to provide a generic self-test controller of a comparatively simple design makes it impractical to deal with such differences within the self-test controller. Accordingly, preferred embodiments of the invention include an interface circuit that performs any necessary signal value and timing adjustments required between the self-test controller and the memory under test. Concentrating the circuit elements required to connect to a particular memory together within an intervening interface circuit allows the design of the self-test controller to remain generic and relatively compact.

[0032] As well as specifying a memory address sequence to be used, a self-test instruction may also additionally specify a data value to be written to a memory during testing. The data value selection can have an important influence upon the type of defects detected by a particular test and may be used to probe the potential vulnerabilities of memories in a way that may be configured by the particular manufacturer or user.

[0033] It will be appreciated that many modern integrated circuits often include multiple different memories. These different memories may have quite different designs and require different test methodologies. The programmable nature of the self-test controller allows this single circuit to test such different memories in a way best suited to the particular memory concerned. The self-test instructions may also specify the way in which any detected errors are to be reported. This is an advantageous feature that allows the error reporting to be tuned to a particular manufacturer's requirement or even to reflect different test environments, such as design debugging compared with manufacturing test.

[0034] Additional data may be recovered concerning detected errors if the interface circuit is provided with a storage which may be accessed under control of a self-test instruction. This simplifies the interface between the self-test controller and the memory and yet allows powerful diagnostic or other data to be captured if a particular user or design makes this desirable.

[0035] In order to efficiently deal with the common circuit variant of differing memory sizes, such as different cache sizes or on-chip RAM sizes, preferred embodiments provide that the self-test instruction should specify the size of the memory being tested.

[0036] In order to reduce the connection overhead associated with the self-test controller preferred embodiments serially load the self-test instructions into the self-test controller.

[0037] The self-test controller is desirably provided with a plurality of external signal pins on the integrated circuit package to facilitate manufacturing test in a way that is independent of other circuit elements.

[0038] Viewed from another aspect the present invention provides a method of testing a memory having a plurality of memory storage locations associated with respective memory addresses, said method comprising the steps of:

[0039] passing a self-test instruction to a self-test controller coupled to said memory; and

[0040] in response to said self-test instruction, performing at least one memory access to each memory location within a sequence of memory storage locations, memory address changes between successive memory locations accessed within said sequence of memory storage locations being selected in dependence upon said self-test instruction such that said self-test controller may be configured by said self-test instruction to perform different memory test methodologies.

[0041] The above, and other objects, features and advantages of this invention will be apparent from the following detailed description of illustrative embodiments which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 schematically illustrates an integrated circuit incorporating a processor core, multiple memories and a self-test controller.

[0043]FIG. 2 schematically illustrates a self-test controller, an interface circuit and a memory in more detail;

[0044]FIG. 3 is a flow diagram schematically illustrating the use of the self-test controller of FIG. 2;

[0045]FIG. 4 schematically illustrates a mapping of physical memory address signals to logical memory address signals; and

[0046]FIG. 5 illustrates in more detail a particular example of an address signal mapping that may be required.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047]FIG. 1 shows an integrated circuit 2 incorporating a processor core 4, a cache memory 6 and an RAM memory 8 (in this example SDRAM). It will be appreciated that such an integrated circuit 2 will typically include many more circuit elements, but these have been omitted from this drawing for the sake of simplicity and clarity.

[0048] A self-test controller 10 is provided on the integrated circuit 2 and communicates with each of the cache memory 6 and the SDRAM memory 8 by a respective dispatch circuit 12, 14. These dispatch circuits act as interface circuits between the self-test controller 10 and the respective memories. Thus, generic memory test driving signals produced by the self-test controller can be re-mapped to logical addresses and adjusted in value and timing to the requirements of the different memories without a need to change the fundamental design of the self-test controller 10.

[0049] It will also be seen that the self-test controller 10 includes a self-test interface 16 provided in the form of multiple external signal pins of the integrated circuit 2. In this way, when the integrated circuit 2 has been fabricated, it may be plugged into an appropriate test controller that initiates the self-test action of the self-test controller 10 and responds to any detected memory defects by either rejecting the integrated circuit 2 as a whole or applying appropriate repairs in circuits where this is possible.

[0050]FIG. 2 schematically illustrates the relationship between the test controller 10 and a memory device 18 in more detail. The self-test controller 10 includes a self-test instruction register 20 into which self-test instructions can be loaded via the self-test interface 16 using serial shifting techniques. Once the self-test instruction is in place, self-test action may be triggered by assertion of an appropriate externally applied signal, such as MBIST_RUN. Within the self-test controller 10 a state machine 22 is responsive to a pattern selection portion of the self-test instruction which serves to select which physical memory address sequence will be generated by the self-controller 10 for application to the memory device 18. As examples, the patterns selected may serve to perform the following actions:

[0051] write a specified data word into all entries;

[0052] read a data word from all entries;

[0053] write a data word or inverse data word in a checkerboard pattern into all entries;

[0054] read a data word or inverse data word in a checkerboard pattern from all entries;

[0055] perform a march C test (this type of test is well known in the memory test field and will not be described herein further);

[0056] perform a read operation and then a write operation using an increment decrement word line fast march;

[0057] perform a read operation and then a write operation using an increment decrement bit line fast march;

[0058] perform a read operation, a write operation and a read operation using an increment decrement word line fast march;

[0059] perform a read operation, a write operation and a read operation using an increment decrement bit line fast march;

[0060] perform a “bang” test which serves to stress test bit line pairs by repeated write operations and read operations;

[0061] perform a predefined suite of tests (such as those mentioned above) to yield a go/no go result; and

[0062] perform a pattern which creates false read data at specific points in order to validate fail detection.

[0063] The data word that may be applied as part of the above described techniques is also supplied as a bit field within the self-test instruction. An engine-control field within the self-test instruction serves to define error reporting options for the self-test controller 10 and self-test system as a whole. An array selection portion of the self-test instruction serves to select which particular memory device is to be tested with the self-test instruction concerned in an environment containing multiple memory devices. It will be appreciated that a self-test instruction could be applied to multiple memory devices in parallel in appropriate circumstances.

[0064] The self-test controller 10 generates physical memory address signals in the form of column address signals and row address signals that are passed to a dispatch controller 24. The data word to be applied in the specified test is also passed to the dispatch controller 24. Various other control signals are also exchanged between the self-test controller 10 and the dispatch controller 24.

[0065] The dispatch controller 24 acts as an interface circuit for applying any necessary signal value adjustments or timing adjustments to the signals generated by the generic self-test controller 10 that are required in order to drive the desired test within the memory device 18. As an example, different latencies of signals may be accommodated by incorporating different lengths of pipeline delay between memory access instructions being received and being serviced. A further significant role of the dispatch controller 24 is to map the physical memory address signals generated by the self-test controller 10 into required logical memory address signals that may drive the memory device 18. In the case where the dispatch controller 24 has been specifically designed for the particular memory device 18, then this mapping may be incorporated into that design. In other embodiments, it may be that the dispatch controller 24 itself is generic to some degree and it is desirable to be able to deal with different mappings that may be necessary. This may be optionally accommodated by latching the physical memory address signals, supplying these to a further separately designed and provided mapping circuit 26, before the desired logical memory address signals are returned and latched within the dispatch controller 24. This separately provided mapping circuit 26 is illustrated within a dotted line within FIG. 2 to demonstrate its optional character. It will be appreciated that the mapping circuit may be separately provided in this way or may be incorporated within the dispatch controller 24. Both of these possibilities are encompassed within the present technique.

[0066] The dispatch controller 24 provides signal values necessary to drive the test within the memory device 18. These signals include a logical address value, a data value, which will typically be an expanded form of the data word as specified within the self-test instruction, and any associated control signals. The dispatch controller 24 will also monitor the response of the memory device 18 to the requested memory access operations and report detected memory defects, such as an incorrect data bit being read back, to the self-test controller 10. The dispatch controller 24 may include data registers that serve to log data specifying any detected errors or other parameters. This data may be read from the dispatch controller 24 to the outside environment using an appropriate self-test instruction scanned into the self-test controller 10 after the testing is complete. This type of operation is particularly useful in design debugging where a fine level of detail regarding detecting errors may be required.

[0067]FIG. 3 is a flow diagram schematically illustrating operation of the embodiments illustrated in FIGS. 1 and 2. At step 28 a self-test instruction is serially loaded into the self-test controller 10. At step 30 control is passed to the self-test controller 10 by the external application of the MBIST_RUN signal illustrated in FIG. 1. At step 32, the state machine 22 within the self-test controller reads the pattern select bits, the engine control bits and the data word bits from the self-test instruction stored within the self-test instruction register 20 and then generates the specified test signals at step 34. It will be appreciated that the self-test instruction will typically specify a long sequence generating many thousands of physical memory address signal values and data values to be applied to the memory device under test to carry out at least part of a desired test methodology.

[0068] After the particular self-test instruction has completed execution, a test at step 36 is made as to whether a pass result or a fail result has been returned. If a fail result has been returned, then processing proceeds to step 38 at which any desired fail action is triggered. If the result was a pass then the processing of the particular self-test instruction terminates directly.

[0069] It will be appreciated that the flow diagram of FIG. 3 illustrates the execution of a single self-test instruction. In practice, a test methodology will typically be built up by a manufacturer or user in the form of a long sequence of such self-test instructions as required to specify a test methodology specially adapted to that particular design and fabrication environment. Thus, multiple self-test instructions will be loaded into the self-test controller 10 and multiple passes through the processing illustrated in FIG. 3 will be made. Data retention, read disturb and iddq testing are supported to be controlling the pattern set.

[0070] It will be appreciated that some users may not wish to custom specify their own test methodology and accordingly may rely upon the default test methodology mentioned above which could be specified using a single self-test instruction and return a single simple go/no go result value.

[0071]FIG. 4 illustrates the receipt of physical memory address signals 40 from the self-test controller 10. These are manipulated by a mapping circuit 42 to generate appropriate logical memory address signals 44 that can drive the memory device under test. In a simple arrangement there may be a one to one mapping of the physical memory address signals to the logical memory address signals. However, in more complicated situations the relationship between physical memory address signals and logical memory address signals may be more complex, but nevertheless readily achievable with a comparatively simple and easy to design mapping circuit 42.

[0072]FIG. 5 illustrates an example of an address signal mapping that may be provided. The memory device under test is formed of two memory arrays each containing 32 rows and 8 columns. The logical address is a 9-bit value. The most significant logical address bit LA[8] is used to control a multiplexer to select between the two arrays of memory. The least significant 3-bits of the logical address LA[2:0] is used to select the column. The remaining logical address bits LA[7:3] are used to select the row. This relationship and arrangement is illustrated at the top of FIG. 5.

[0073] The middle portion of FIG. 5 is similar to FIG. 2. This illustrates a macrocell which may be part of a SOC design (and have its own an SOC interface), which also includes a self-test controller 10, a dispatch controller 24 as well as the memory device formed of the two blocks as discussed above. The self-test controller 10 treats the memory device as an array of memory locations having 32 rows as represented by the 5-bit row address Xaddr. The column of the memory locations is expressed as the Yaddr 4-bit address irrespective of whether this column is in the lower order block or the higher order block within the physical device. In the example of FIG. 5 the mapping circuit is provided externally of the dispatch controller 26 via a custom circuit attached to the SOC interface. Attaching the custom mapping circuit at this level allows easy alteration to this circuit and design of this circuit. In the example illustrated, the physical memory address signals are latched within the dispatch circuit 24 and then passed out to the separate mapping circuit. Within the mapping circuit the least significant 3-bits of the Yaddr field form the least significant 3-bits of the logical address LA[2:0]. The most significant bit of the Yaddr value forms the most significant bit LA[8] of the logical address. The row address 5-bit value Xaddr forms the bits LA[7:3] of the logical address. The logical address LA [8:0] built up in this way is passed back from the mapping circuit into the dispatch controller 24 and again latched prior to being applied to the memory device to perform the desired test.

[0074] A further more detailed description of the above techniques is given as follows:

[0075] Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims. 

We claim:
 1. Apparatus for processing data, said apparatus comprising: at least one memory having a plurality of memory storage locations associated with respective memory addresses; and a self-test controller operable to control self-test of said at least one memory; wherein said self-test controller is responsive to a self-test instruction to perform at least one memory access to each memory location within a sequence of memory storage locations, memory address changes between successive memory locations accessed within said sequence of memory storage locations being selected in dependence upon said self-test instruction such that said self-test controller may be configured by said self-test instruction to implement different memory test methodologies.
 2. Apparatus as claimed in claim 1, wherein said self-test controller is operable to execute a plurality of self-test instructions to perform a sequence of memory tests, said self-test instructions being programmable to allow different sequences of memory tests to be specified by different users.
 3. Apparatus as claimed in claim 2, wherein said sequence of memory tests may be changed to match different memories.
 4. Apparatus as claimed in claim 2, wherein said sequence of memory tests may be changed to match different fabrication characteristics and test needs.
 5. Apparatus as claimed in claim 1, wherein said memory addresses are physical row and column addresses within said at least one memory.
 6. Apparatus as claimed in claim 1, wherein said self-test instruction specifies data to be written to said memory as part of said at least one memory access.
 7. Apparatus as claimed in claim 1, wherein said memory address changes between successive memory locations as selected in dependence upon said self-test instruction and said self-test controller allow one or more of the following memory test operations to be performed: (i) write specified data to all memory locations within a range of memory addresses; (ii) read data from all memory locations within a range of memory addresses; (iii) write specified data to memory locations having a checkerboard pattern of memory addresses; (iv) read data from memory locations having a checkerboard pattern of memory addresses; (v) conduct a march C memory test; (vi) read data from and write specified data to a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a row of memory locations are accessed in turn before a next row of memory locations is selected for access; (vii) read data from and write specified data to a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a column of memory locations are accessed in turn before a next column of memory locations is selected for access; (viii) read data from, write specified data to and read data from a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a row of memory locations are accessed in turn before a next row of memory locations is selected for access; (ix) read data from, write specified data to and read data from to a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a column of memory locations are accessed in turn before a next column of memory locations is selected for access; (x) for a sequence of memory locations, repeatedly write a value to one or more bitlines within said memory and then read a complementary value stored within a memory location sharing said one or more bitlines; and (xi) for a sequence of memory locations, repeatedly read a value from a memory location while interjecting opposing data writes; (xii) a predetermined combination of memory test operations as defined in (i) to (xi) for go/nogo testing where manufacture's test methods do not have specific requirements; and (xiii) creating false read data at specific points in order to validate fail detection.
 8. Apparatus as claimed in claim 1, further comprising a processor core, said processor core, said at least one memory and said self-test controller being formed together on an integrated circuit.
 9. Apparatus as claimed in claim 1, wherein said at least one memory is one of a synthesized memory and a custom memory.
 10. Apparatus as claimed in claim 1, wherein an interface circuit is disposed between said self-test controller and said at least one memory, said interface circuit serving to adapted values and timings of signals passed between said self-test controller and said at least one memory to accommodate differing value and timing properties of said at least one memory.
 11. Apparatus as claimed in claim 10, wherein said interface circuit maps a memory address value generated by said self-test controller to a logical address value to be input to said at least one memory.
 12. Apparatus as claimed in claim 1, comprising a plurality of memories and said self-test instruction specifies to which of said plurality of memories said self-test instruction is to be applied.
 13. Apparatus as claimed in claim 1, wherein said self-test instruction specifies in which of a plurality of different ways a detected memory error is to be reported by said self-test controller.
 14. Apparatus as claimed in claim 10, wherein said interface circuit includes a result data register in which result data from testing said at least one memory may be captured and said self-test controller is responsive to a self-test instruction to read result data from said result data register.
 15. Apparatus as claimed in claim 1, wherein said self-test instruction specifies a size of said at least one memory to be tested.
 16. Apparatus as claimed in claim 1, wherein said self-test instruction is serially loaded into said self-test controller.
 17. Apparatus as claimed in claim 1, wherein said at least one memory and said self-test controller are formed together on an integrated circuit having a plurality of external signal pins, said self-test controller having one or more external signal pins through which one or more self-test instructions may be applied to said self-test controller.
 18. A method of testing a memory having a plurality of memory storage locations associated with respective memory addresses, said method comprising the steps of: passing a self-test instruction to a self-test controller coupled to said memory; and in response to said self-test instruction, performing at least one memory access to each memory location within a sequence of memory storage locations, memory address changes between successive memory locations accessed within said sequence of memory storage locations being selected in dependence upon said self-test instruction such that said self-test controller may be configured by said self-test instruction to implement different memory test methodologies.
 19. A method as claimed in claim 18, comprising executing a plurality of self-test instructions with said self-test controller to perform a sequence of memory tests, said self-test instructions being programmable to allow different sequences of memory tests to be specified by different users.
 20. A method as claimed in claim 19, wherein said sequence of memory tests may be changed to match different memories.
 21. A method as claimed in claim 19, wherein said sequence of memory tests may be changed to match different fabrication characteristics and test needs.
 22. A method as claimed in claim 18, wherein said memory addresses are physical row and column addresses within said at least one memory.
 23. A method as claimed in claim 1, wherein said self-test instruction specifies data to be written to said memory as part of said at least one memory access.
 24. A method as claimed in claim 1, wherein said memory address changes between successive memory locations as selected in dependence upon said self-test instruction and said self-test controller allow one or more of the following memory test operations to be performed: (i) write specified data to all memory locations within a range of memory addresses; (ii) read data from all memory locations within a range of memory addresses; (iii) write specified data to memory locations having a checkerboard pattern of memory addresses; (iv) read data from memory locations having a checkerboard pattern of memory addresses; (v) conduct a march C memory test; (vi) read data from and write specified data to a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a row of memory locations are accessed in turn before a next row of memory locations is selected for access; (vii) read data from and write specified data to a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a column of memory locations are accessed in turn before a next column of memory locations is selected for access; (viii) read data from, write specified data to and read data from a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a row of memory locations are accessed in turn before a next row of memory locations is selected for access; (ix) read data from, write specified data to and read data from to a sequence of memory locations within a memory arranged in rows and columns of memory locations such that memory locations within a column of memory locations are accessed in turn before a next column of memory locations is selected for access; (x) for a sequence of memory locations, repeatedly write a value to one or more bitlines within said memory and then read a complementary value stored within a memory location sharing said one or more bitlines; and (xi) for a sequence of memory locations, repeatedly read a value from a memory location while interjecting opposing data writes; (xii) a predetermined combination of memory test operations as defined in (i) to (xi) for go/nogo testing where manufacture's test methods do not have specific requirements; and (xiii) creating false read data at specific points in order to validate fail detection.
 25. A method as claimed in claim 18, wherein said at least one memory and said self-test controller formed together with a processor core on an integrated circuit.
 26. A method as claimed in claim 18, wherein said at least one memory is one of a synthesized memory or a custom memory.
 27. A method as claimed in claim 18, wherein values and timings of signals passed between said self-test controller and said at least one memory are adapted by an interface circuit disposed between said self-test controller and said at least one memory in order to accommodate differing value and timing properties of said at least one memory.
 28. A method as claimed in claim 27, wherein said interface circuit maps a memory address value generated by said self-test controller to a logical address value to be input to said at least one memory.
 29. A method as claimed in claim 18, wherein said self-test instruction specifies to which of a plurality of memories said self-test instruction applies.
 30. A method as claimed in claim 18, wherein said self-test instruction specifies in which of a plurality of different ways a detected memory error is to be reported by said self-test controller.
 31. A method as claimed in claim 27, wherein said interface circuit includes a result data register in which result data from testing said at least one memory may be captured and said self-test controller is responsive to a self-test instruction to read result data from said result data register.
 32. A method as claimed in claim 18, wherein said self-test instruction specifies a size of said at least one memory to be tested.
 33. A method as claimed in claim 18, wherein said self-test instruction is serially loaded into said self-test controller.
 34. A method as claimed in claim 18, wherein said at least one memory and said self-test controller are formed together on an integrated circuit having a plurality of external signal pins, said self-test controller having one or more external signal pins through which one or more self-test instructions may be applied to said self-test controller. 